The present invention relates to edible fat products suitable for preparing margarines, and more particularly to increasing the solid fat contents of triglyceride oils containing high levels of polyunsaturates and low levels of saturated fatty acids.
It has been known for some time that interesterifying triglyceride oils would enable the production of fat products having increased solid contents at low temperatures. Corn oil, sunflower oil, and safflower oil are examples of oils having high linoleic acid contents and relatively low saturated acid contents. Sunflower oil, for example, can have polyunsaturated fatty acid contents of as high as about 75% with saturated fatty acid contents as low as 7%. Similarly, corn oil can have polyunsaturates as high as 62% and saturates as low as about 12%. In U.S. Pat. No. 2,442,538, Abbott teaches that oils such as these can be employed to prepare margarines by first subjecting them to a directed interesterification process for about 5 days at a minimum temperature of about 40.degree. F., and then partially hydrogenating them to increase the firmness of the products. Unfortunately, the partial hydrogenation of liquid oils results in a formation of trans isomers of oleic acid. Such trans-isomereric forms of fatty acid in the diet are the center of much scientific controversy and the subject of on-going research to determine what role, if any, they play in dietary health.
In U.S. Pat. No. 3,859,447, Sreenivasan discloses that triglyceride oils having high linoleic acid contents and insufficient solid triglycerides to form a plastic margarine, can be subjected to a directed interesterification process at temperatures of 0.degree. to -15.degree. C. using, as a catalyst, an alkali metal alkoxide along with an aprotic substance. Sreenivasan indicates that the combination catalyst allows interesterification to proceed at a higher rate such that an edible fat suitable for the preparation of a plastic margarine can be obtained in 7 days or less without the presence of any hydrogenated material. Unfortunately, this procedure is still quite lengthy and requires presence of aprotic substances, such as dimethyl sulfoxide, which are difficult to handle in a safe manner.
In an article in Fette, Seifen, und Anstrichmittel, Vol. 76, No. 2 (1974), at pages 79-82, Kattenberg describes a study of acceleration of controlled interesterification by periodic variation of the reaction temperature. He indicates that repeated cooling and warm-up steps during interesterification of sunflower oil at low temperatures accelerates the rate of reaction by a factor of about 3. While Kattenberg indicates that the resulting sunflower oil is suitable for the preparation of margarine, experience has shown that sunflower oils in general have saturated fatty acid contents too low to provide sufficient solid triglycerides to form a commercially acceptable margarine for home use.
In U.S. Pat. No. 3,855,254, Haighton et al describe the directed interesterification of liquid triglyceride oils. They disclose that the reaction rates can be accelerated by subjecting a mixture of glycerides alternately to a temperature of 1.degree.-15.degree. C. below the cloud point of a randomized mixture of the same glycerides, and to a temperature of at least the cloud point of that randomized mixture. The temperature is cycled at least three times until the cloud point of the mixture obtained is at least 5.degree. C. above the cloud point of the randomized mixture. Again here, there is shown the preparation of a margarine product, but the dilatation values indicate that it is quite soft without the addition of any hardstock solids.
In Belgian Pat. No. 870,481, there is disclosed a process for the directed transesterification of a triglyceride oil or oil mixture to achieve higher solids contents, melting points and cloud points. The examples disclose the directed transesterification of a number of liquid triglyceride oils which are quite low in saturated fatty acid content. Where it is desired to form a margarine from these oils, the examples indicate that it may be necessary to add crystalline solid fats prior to interesterification. Example X indicates that where a corn oil with a high iodine number is employed as the triglyceride oil, 0.5% of solid fat crystals obtained from a previous directed transesterification can be employed to provide an end product which is said to be suitable as the sole margarine fat component. This procedure, however, requires the processing of an additional amount of the triglyceride oil through the entire cyclic process to obtain the added solids content necessary. This extra processing is less economical than might be desired.